[pups] AVIV vs. DigiData tape controller

[Gregory R. Travis]

Can someone enlighten me regarding DEC SDI cabling?  Here's
what I have:

RA81 disk drive with two big black cables coming out of it, one for
each port (A/B).  The cables terminate at the drive on one end and
at a small metal box on the other end.  The small metal box has
two sockets on it (denoted with "*" in the picture below):

                       Small metal box
                          /
+----------+  "A" cable  /
| RA81     |------------[]*
| Drive    |------------[]*
+----------+  "B" cable


UDA50 controller in 11/44 with four sets of orange cables coming out
of it and terminating in a four-port socket set (denoted "*" in picture
below) in a larger metal box at the back of the cabinet:

                        Larger metal box
                         /
                        /
                     *[]_________
                     *[]_________\
                     *[]_________\\  <- Four (4) Cable groups
                     *[]_________\\\
                                 \\\\
                             ----------
                             | UDA50  |
                             |        |
                             ----------

What I have tried:
	I unscrewed the black cables from the small metal box
	and plugged one of them directly into one of the ports on
	the larger metal box:


+----------+  "A" cable  
| RA81     |----------------|
| Drive    |----------[]*   |
+----------+  "B" cable     |
                           /   Larger metal box
                          /      /
                          |     /
                          |-*[]_________
                            *[]_________\
                            *[]_________\\  <- Four (4) Cable groups
                            *[]_________\\\
                                        \\\\
                                     ----------
                                     | UDA50  |
                                     |        |
                                     ----------


That didn't work (I tried it with two different drives and cable sets).
The operating system (2.11BSD) sees the UDA50 but does not see the drive
(which is spun up and "ready").

I did a little searching on the internet and found a couple of
cryptic discussions.  What I surmised from the discussions was that you
cannot directly connect the drive cable to the bulkhead box on the
computer cabinet.  It seems you need a third cable to act as an
intermediary as such:

                      Small metal box
                         /
+----------+  "A" cable / 
| RA81     |----------[]*---|  
| Drive    |----------[]*   | <--- New THIRD ("external?") cable
+----------+  "B" cable     |
                           /   Larger metal box
                          /      /
                          |     /
                          |-*[]_________
                            *[]_________\
                            *[]_________\\  <- Four (4) Cable groups
                            *[]_________\\\
                                        \\\\
                                     ----------
                                     | UDA50  |
                                     |        |
                                     ----------


Is that right?  If so, where can I find one of these external cables and/or
is it possible to manufacture one from a bit of ribbon cable an a
couple of commonly available plugs?  The sockets denoted by "*" appear to
be AMD bastardizations of common PC board plugs like the ones one would
find connecting a console port plug.

Thanks!

greg

Gregory Travis
Cornerstone Information Systems ATS
greg at ciswired.com
812 330 4361 ext. 18